The invention relates generally to gas flowmeters and more specifically concerns calibrating hydrocarbon gas flowmeters.
Gas flowmeters are widely used in various scientific and industrial applications. Their efficient use requires frequent calibrations. Such routine calibrations are generally easy except when the gases involved are rare/toxic or highly reactive. Most of the hydrocarbons, however, fall in the latter category and often call for special calibration equipment and procedures.
Flowmetry of gaseous hydrocarbons has always been a challenging problem. Normally, the flowmeters used for hydrocarbons are calibrated for air and require a special calibration factor for each hydrocarbon, depending on the physical principle involved in the operation of the flowmeter.
There are many types of flowmeters in use today. These include among others turbine flowmeters, variable area flowmeters, head type flowmeters, ultrasonic mass flowmeters and thermal flowmeters. All flowmeters are normally calibrated for air and then used for other gases with the help of conversion/correction factors provided by the manufacturer. For thermal flowmeters, these conversion factors F are calculated by dividing the specific heat C.sub.P of air at standard temperature and pressure (STP) by the specific heat C.sub.P of the test gas at STP. However, experimentally determined values of F are not always in agreement with the calculated values, mainly because C.sub.P values for most hydrocarbons vary significantly with temperature and pressure and are not constant across the test element. For this reason, it is always advisable to use experimentally determined values of F--particularly in high accuracy investigations. This, however, is not always feasible--particularly when the gases are toxic or rare. Hydrocarbons which are widely used in aeronautical and/or combustion kinetics laboratories fall in the group of gases for which calibration is not routinely performed. More often than not, one has to contend with the calculated values of the gas conversion factors which suffer from their inherent inaccuracies for the reasons cited above.
It is an object of the invention to provide a technique for obtaining the gas conversion factors for flowmeters.
Another object of this invention is to provide a technique for experimentally obtaining hydrocarbon gas conversion factors for flowmeters.
A further object of this invention is to provide a technique for obtaining the toxic or rare gas conversion factors for flowmeters.
Other objects and advantages of this invention will become apparent hereinafter in the specification and drawing.